The Pentagon urged a peaceful resolution Tuesday to the hijacking of a freighter off Somalia but said US warships were there to make sure pirates do not make off with its cargo of Russian tanks and other weapons.

Several US warships had the Belize-flagged MV Faina "contained," said Geoff Morrell, the Pentagon press secretary. He would not comment on whether the navy has plans to liberate the 21 crew members held captive by pirates.

"We clearly have a number of navy vessels, warships, if you will, in the vicinity, which have enormous capabilities on them," he said.

"But at this point, what we are most concerned about is seeing a peaceful solution to this problem," he said.

A Russian warship was reported to be heading to the scene, adding a new wrinkle to the standoff.

Morrell, who said it was expected to take several days for the Russian ship to arrive, said the US Navy had enough ships to handle the situation.

"But this involves Russian cargo, as I understand it, so I don't think that we have a particular issue with the Russians coming on the scene, as well," he said.

Somali pirates seized the Ukrainian-owned ship last week, and are demanding 20 million dollars ransom.

Morrell said the US Navy was not negotiating with the pirates, and he did not know who was. But he said the payment of a ransom was not a major concern.

"Our concern is right now making sure that there's a peaceful resolution to this, that this cargo does not end up in the hands of anyone who would use it in a way that would be destabilizing to the region.

"And we have committed significant resources to make sure that those two objectives are met," he said.

Kenya has said it is the intended recipient of the cargo, denying reports that it was bound for Sudan.